1. Field
Example embodiments relate to a method of manufacturing an image sensor having an air gap, and more particularly, to a method of manufacturing a back-illuminated image sensor in which a light receiving unit is formed on a rear surface. Example embodiments further relate to a method of manufacturing an image sensor in which a reflection pattern is formed on a dielectric layer to improve optical sensitivity of a light receiving unit formed on a rear surface. Additional embodiments relate to a method of manufacturing an image sensor in which a reflection pattern is formed simultaneously with an interconnection pattern. Other embodiments relate to a method of manufacturing an image sensor that may reduce or alternatively prevent optical crosstalk caused by incidence of light reflected by a reflection pattern to an adjacent pixel. Alternative embodiments relate to a method of manufacturing an image sensor having an air gap in which when tilted light is reflected by a reflection pattern and incident to an adjacent cell, the air gap may totally reflect the light and guide the light to a corresponding pixel.
2. Description of Related Art
In general, an image sensor is a photoelectric conversion device configured to sense light and convert the light into an electrical signal. A typical image sensor may include a plurality of pixels arranged in a matrix shape on a semiconductor substrate. Each of the pixels may include a photodiode (PD) and transistors. A semiconductor layer and the PD disposed on the semiconductor substrate may sense external light and generate photocharges. The generated photocharges may be collected in the PD. Also, the transistors may output an electrical signal according to the amount of the generated photocharges.
However, in the case of the image sensor, the generated photocharges may be transmitted to and accumulated in a photoelectric conversion device of an adjacent pixel, thereby causing crosstalk between the pixels.
The crosstalk may be classified into optical crosstalk and electrical crosstalk. The optical crosstalk may occur when incident light passing through a microlens (ML) and a color filter is transmitted to a photoelectric conversion device of an adjacent pixel other than a corresponding pixel due to refraction light refracted by an interlayer dielectric (ILD) having a different refractive index from the incident light or reflection light reflected by a top or lateral surface of a metal interconnection layer. The electrical crosstalk may occur when charges generated by a lower or lateral portion of a photoelectrical conversion unit are transmitted to a photoelectric conversion device of an adjacent pixel due to incident light having a long wavelength.
When crosstalk occurs, a black-and-white image sensor may suffer from image distortion due to its low resolution. Also, a color image sensor, which uses a color filter array (CFA) having red, green, and blue filters, may be highly likely to suffer from crosstalk due to red incident light having a long wavelength, thereby causing tint failures. Also, blooming may occur between adjacent pixels on a screen.
Image sensors have recently shown an increasing tendency to become highly integrated. Thus, a distance between pixels and the size of PDs is also decreasing. Thus, with an increase in the integration density of image sensors, crosstalk may become more problematic.